Summary: A Geometry-based Soft Shadow Volume Algorithm
using Graphics Hardware
Ulf Assarsson Tomas Akenine-M¨oller
Chalmers University of Technology
Sweden
Abstract
Most previous soft shadow algorithms have either suffered from
aliasing, been too slow, or could only use a limited set of shadow
casters and/or receivers. Therefore, we present a strengthened soft
shadow volume algorithm that deals with these problems. Our crit-
ical improvements include robust penumbra wedge construction,
geometry-based visibility computation, and also simplified com-
putation through a four-dimensional texture lookup. This enables
us to implement the algorithm using programmable graphics hard-
ware, and it results in images that most often are indistinguishable
from images created as the average of 1024 hard shadow images.
Furthermore, our algorithm can use both arbitrary shadow casters
and receivers. Also, one version of our algorithm completely avoids
sampling artifacts which is rare for soft shadow algorithms. As a
bonus, the four-dimensional texture lookup allows for small tex-